JP4220352B2 - Fuel supply system for liquefied gas engine - Google Patents

Description

  The present invention relates to a fuel supply apparatus for a liquefied gas engine that uses liquefied gas such as dimethyl ether as fuel.

  In recent years, dimethyl ether (hereinafter abbreviated as DME), which smokelessly burns with a high cetane number (55 or more), has been attracting attention as an alternative fuel for petroleum and light oil, and in particular, achieved low NOx with EGR (exhaust gas recirculation) and catalysts. From the viewpoint of satisfying strict exhaust regulations in the future, studies are underway as alternative fuels for diesel engines.

  However, since DME has a characteristic that its boiling point is as low as −25 ° C. and is easy to evaporate, the characteristics of DME are fully taken into consideration in the practical use of a DME engine using DME as fuel. It is considered that a fuel supply device is required. For example, a fuel supply device for a DME engine as shown in FIG. 2 has already been proposed.

  In the example shown here, the fuel (DME) stored in the fuel tank 1 at a pressure of about 0.4 to 1 MPa is sent to the feed line 3 by the feed pump 2 and installed in the middle of the feed line 3. The high pressure pump 4 increases the pressure to about 15 to 50 MPa and accumulates the pressure in the common rail 5. The fuel is guided from the common rail 5 to the injector 7 of each cylinder through the injection line 6 and injected into the combustion chamber 8 by valve opening control. It is made to burn by compression ignition as in the case of a normal diesel engine.

  In addition, when the pressure exceeds a predetermined value in the fuel gallery in the high-pressure pump 4, surplus fuel is released to the return line 3 ′ via the overflow valve and returned to the fuel tank 1.

  In such a fuel supply device, when the flow of the fuel stops when the engine is stopped, heat is transmitted from the engine side, the temperature of the fuel in the system rises, and the common rail 5 side expands due to the temperature rise of the fuel. However, since the fuel remaining in the nozzle of the injector 7 having particularly severe thermal conditions is vaporized, the fuel from the injector 7 to which pressure from the common rail 5 side is continuously applied is burned. Leak into the gas (it is difficult to seal the gas leak even if it is liquid-tight), and the leaked vaporized gas accumulates in the combustion chamber 8 and may cause abnormal combustion the next time the engine is started. There is.

  Therefore, in order to avoid such abnormal combustion, a purge line 11 is provided for extracting fuel from the common rail 5 by the purge control valve 9 and returning it to the fuel tank 1 through the check valve 10 when the engine is stopped. In the example shown here, a branch line 13 is also provided for extracting fuel from the downstream side of the purge control valve 9 of the purge line 11 and leading it to the purge tank 12.

  That is, when the fuel in the common rail 5 is recovered in the fuel tank 1, the pressure on the common rail 5 side gradually decreases and it becomes difficult for the fuel to flow into the fuel tank 1 side. 14 is opened and the remaining fuel is recovered from the fuel tank 1 side to the low pressure purge tank 12, and the fuel extracted to the purge tank 12 and decompressed to 0 to 0.3 MPa is recirculated by the compressor 16 through the communication line 15. It is liquefied and returned to the fuel tank 1.

The prior art document information related to this type of liquefied gas engine fuel supply apparatus includes the following information by the same applicant as the present invention.
JP 2003-56393 A JP 2003-56409 A

  However, when the fuel supply device for a liquefied gas engine as described above is used under engine operating conditions with a high ambient temperature, such as under high outdoor temperature conditions such as in summer or under high engine room temperature conditions, Since the fuel cannot be sufficiently cooled and vaporizes due to a temperature rise, there is a problem that the fuel cannot be stably injected into the cylinder of the engine in a liquid state.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a fuel supply apparatus for a liquefied gas engine that can stably inject fuel into a cylinder of an engine in a liquid state even under high temperature conditions. .

According to a first aspect of the present invention, there is provided a liquefied gas engine in which fuel introduced from a fuel tank is boosted by a high-pressure pump and accumulated in a common rail, and fuel is introduced from the common rail to an injector at the top of a cylinder and injected into a combustion chamber. In the fuel supply device,
With a heat exchangeable purge tank line from the fuel tank to the high pressure pump,
A first purge line connected to the purge tank for returning hot fuel from the high pressure pump to the purge tank and extending from the common rail to return hot fuel from the common rail to the purge tank; A second purge line connected to the purge tank,
Wherein the purge tank, relates to a fuel supply system, the liquefied gas engine, characterized by being configured so as to cool the fuel to the high pressure pump by the latent heat of evaporation of the heated fuel by air the heated fuel is there.

According to a second aspect of the present invention, a fuel injector for a liquefied gas engine according to claim 1, wherein a sub-injector is provided in an intake passage that guides intake air to the cylinder, and fuel extracted from the purge tank is guided to the sub-injector. , Related to

  Thus, according to the present invention, the high temperature fuel is returned to the purge tank and vaporized to cool the fuel to the high pressure pump by the latent heat of vaporization of the high temperature fuel. Even when it is used, the fuel directed to the engine is sufficiently cooled to prevent the vaporization of the fuel, and can be stably injected into the cylinder of the engine in a liquid state.

  When the high temperature fuel is returned from the high pressure pump to the purge tank, the high temperature fuel is returned from the high pressure pump and cooled sufficiently in the purge tank even when used under engine operating conditions where the ambient temperature is high. Is sent to the high-pressure pump, so that fuel vaporization in the high-pressure pump can be prevented, and the liquid can be stably injected into the cylinder of the engine.

  By configuring the high temperature fuel to return to the purge tank from the common rail, the high temperature fuel is returned from the common rail and the fuel sufficiently cooled by the purge tank is returned to the common rail even when used under engine operating conditions where the ambient temperature is high. Therefore, fuel vaporization on the common rail can be prevented, and the fuel can be stably injected into the cylinder of the engine in a liquid state.

  If a sub-injector is provided in the intake passage that guides intake air to the cylinder and the fuel extracted from the purge tank is guided to the sub-injector, a part of the fuel to be supplied to the combustion chamber is distributed to the sub-injector side. By reducing the amount of fuel to be injected from the injector at the top, the injection time is shortened. As a result, the amount of fuel that burns at a timing that is difficult to convert to output is greatly reduced, increasing the thermal efficiency of the engine and greatly improving fuel efficiency Can be improved.

  According to the fuel supply device for a liquefied gas engine of the present invention described above, since a part of the fuel is vaporized by the purge tank and the fuel is cooled by latent heat of vaporization, the vaporization of the fuel toward the engine is prevented and the engine is in a liquid state It is possible to achieve an excellent effect that the fuel can be stably injected into the cylinder.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an embodiment for carrying out the present invention, and the same reference numerals as those in FIG. 2 denote the same components.

  In the fuel supply apparatus of the liquefied gas engine of this embodiment, a feed line 17 for sending fuel (DME) from the fuel tank 1 to the high pressure pump 4 between the fuel tank 1 and the high pressure pump 4 and fuel in the high pressure pump 4 A return line 18 is provided for returning surplus fuel to the fuel tank 1 when the pressure exceeds a predetermined value in the gallery. The feed line 17 includes, in order from the fuel tank 1 side, a feed pump 19 in the fuel tank 1, A first fuel cooler 20, a purge tank 21, a fuel pressure sensor 22, and a first fuel temperature sensor 23 are provided, and a check valve 24 and a second fuel cooler 25 are sequentially provided on the return line 18 from the high-pressure pump 4 side. The second fuel temperature sensor 26 is provided.

  Here, in a portion of the feed line 17 located in the purge tank 21, the pipe 27 of the feed line 17 is bent in a loop shape or the like so that heat can be exchanged between the fuel in the purge tank 21 and the fuel in the feed line 17. Alternatively, the pipe 27 of the feed line 17 is provided with fins or the like so that heat exchange is possible.

  Also, a first purge line 28 connected to the purge tank 21 is provided between the second fuel temperature sensor 26 and the fuel tank 1 in the return line 18. A flow rate adjusting valve 29 is provided at a position, and an injection nozzle 30 is provided from the inlet of the purge tank 21 toward the inside of the purge tank 21.

  Further, the common rail 5 is provided with a second purge line 31 connected to the purge tank 21, and the second purge line 31 is provided with a purge valve 32 at an intermediate position.

  On the other hand, a sub-injector 35 is newly provided in the intake manifold that forms the intake passage 34 that guides the intake air 33 to each cylinder. Here, the sub-injector 35 is arranged for each cylinder so as to be located on the inlet side of the intake port of each cylinder. For example, the sub-injector 35 may be provided near the end of the intake pipe connected to the intake manifold. In this case, the sub-injector 35 may be arranged alone.

  The purge tank 21 is provided with a third fuel temperature sensor 36 for measuring the internal temperature, and is provided with a premixing line 37 connected to the sub-injector 35 and a reliquefaction line 38 connected to the fuel tank 1. The reliquefaction line 38 is provided with a reliquefaction pump 39 and a third fuel cooler 40 in order from the purge tank 21 side.

  The operation of the embodiment for carrying out the present invention will be described below.

  When driving the fuel supply device of the liquefied gas engine of this embodiment, liquid fuel is supplied from the fuel tank 1 to the high-pressure pump 4 via the feed line 17, the purge tank 21 and the like by the feed pump 19, and the common rail 5. When the pressure exceeds the predetermined value in the fuel gallery in the high-pressure pump 4, the flow rate adjustment valve 29 of the first purge line 28 is closed to remove excess fuel from the return line. Return to the fuel tank 1 via 18.

  On the other hand, the fuel in the high-pressure pump 4 becomes high when used under conditions of high outside air temperature such as summer, or under high engine room temperature and under high engine operating conditions. The flow rate adjustment valve 29 of one purge line 28 is opened, and high temperature fuel is supplied from the high pressure pump 4 to the purge tank 21 via the return line 18 and the first purge line 28, and the second fuel cooler 25. Then, the fuel is cooled and sprayed into the purge tank 21 by the spray nozzle 30. Further, the fuel in the common rail 5 becomes high temperature under engine operating conditions where the ambient temperature is high. Therefore, the purge valve 32 of the second purge line 31 is opened, and high temperature fuel is supplied from the common rail 5 to the second purge line. The gas is supplied to the purge tank 21 via the gas supply 31 and supplied into the purge tank 21.

  When the high-temperature fuel is introduced into the purge tank 21, it vaporizes with the characteristics of the fuel itself that is easily vaporized and cools the purge tank 21 by latent heat of vaporization. By cooling the inside of the purge tank 21, heat is exchanged between the gaseous fuel introduced into the purge tank 21 and the liquid fuel in the feed line 17, and the liquid fuel in the feed line 17 is positively exchanged. Cool. Here, the liquid fuel in the feed line 17 cooled by heat exchange is supplied to the high-pressure pump 4 and guided to the common rail 5 and the injector 7.

  On the other hand, the gaseous fuel in the purge tank 21 is appropriately supplied to the sub-injector 35 via the pre-mixing line 37, and the fuel supplied to the sub-injector 35 is used for pre-mixing to the intake manifold. Combusted in combination with liquid fuel injection into the cylinder. If the fuel vaporized in the purge tank 21 is large, the fuel is sent to the reliquefaction line 38, liquefied by the reliquefaction pump 39, and returned to the fuel tank 1. Further, when the outside air temperature is low, such as in winter, or when the engine room temperature is low, the flow control valve 29 and the purge valve 32 of the first purge line 28 are adjusted to adjust the inside of the purge tank 21. The fuel to be introduced is reduced.

Here, in order to show the temperature drop when the fuel (DME) is vaporized, together with the basic data [Table 1] of the fuel (DME) and light oil,
[Table 1]
DME Light oil latent heat of vaporization kJ / kg 467.13 300
Boiling point (@ 1 at) ° C -25 180-360
Specific heat Cp kJ / kg · K 2.99 1.7
Liquid density g / cc 0.67 0.83
When 1 kg of DME is vaporized, the latent heat of vaporization / specific heat = 467.13 / 2.99 = 156 to 1 kg of DME becomes a heat amount of about 156 ° C., and the amount of heat is entirely the temperature of the fuel. As used for change, when 20% of the total is vaporized, 80% of the liquid fuel is reduced by about 40 ° C.

  Thus, according to the fuel supply apparatus of the liquefied gas engine of this embodiment, the piping of the feed line 17 that can exchange heat by the latent heat of vaporization of the high-temperature fuel by returning the high-temperature fuel to the purge tank 21 and vaporizing it. 27, the fuel to the high-pressure pump 4 is cooled, so that the fuel is used under engine operating conditions with a high ambient temperature, such as under high outdoor temperature conditions such as in summer or under high engine room temperature conditions. However, the fuel directed to the engine can be sufficiently cooled to prevent vaporization of the fuel, and can be stably injected into the engine cylinder in a liquid state. Moreover, since the inside of the purge tank 21 is cooled by the pressure reduction by the reliquefaction pump 39 of the reliquefaction line 38, the fuel to the high pressure pump 4 can be cooled further. Furthermore, when the fuel vaporized or liquefied in the purge tank 21 is large, the fuel is fed to the reliquefaction line 38 and returned to the fuel tank 1, so that an excessive burden on the purge tank can be suppressed. Furthermore, when the outside air temperature is low, such as in winter, the fuel to be introduced into the purge tank 21 is reduced by adjusting the flow rate adjustment valve 29 and the purge valve 32, so that the reliquefaction line 38 and the reliquefaction pump 39. It is possible to reduce the re-liquefaction treatment via, and to reduce energy loss.

  If the high temperature fuel is returned from the high pressure pump 4 to the purge tank 21, the high temperature fuel is returned from the high pressure pump 4 and the purge tank 21 is sufficient even when used under engine operating conditions with a high ambient temperature. Since the cooled fuel is sent to the high-pressure pump 4, the fuel is prevented from being vaporized by the high-pressure pump 4 and can be stably injected into the cylinder of the engine in a liquid state.

  If the high temperature fuel is returned from the common rail 5 to the purge tank 21, the high temperature fuel is returned from the common rail 5 and sufficiently cooled by the purge tank 21 even when the engine is used under engine operating conditions with a high ambient temperature. Since the spent fuel is sent to the common rail 5, the vaporization of the fuel in the common rail 5 can be prevented, and the fuel can be stably injected into the cylinder of the engine in a liquid state.

  If a sub-injector 35 is provided in the intake passage 34 that guides the intake air 33 to the cylinder and the fuel is guided from the purge tank 21 to the sub-injector 35, a part of the fuel to be supplied into the combustion chamber 8 is sub-injector 35. Therefore, the amount of fuel to be injected from the injector 7 at the top of the cylinder is reduced to shorten the injection time. As a result, the amount of fuel combusted at a timing that is difficult to be converted to output is greatly reduced. The fuel efficiency can be greatly improved by increasing the thermal efficiency. In the cylinder, the premixing of the fuel is promoted by the prior injection of the vaporized gas from the sub-injector 35, and the fuel is injected from the injector 7 to the intake air 33 (mixed gas) in the accelerated state. Fuel diffuses and spreads throughout the chamber 8, and a good dispersion and mixing state is obtained, and the combustibility in the cylinder is greatly improved. As a result, the combustion temperature is kept relatively low and NOx is generated. Can be reduced.

  The fuel supply device for the liquefied gas engine of the present invention is not limited to the above-described embodiment. The fuel may be a liquefied gas fuel other than dimethyl ether, and the temperature of the fuel temperature sensor. Each fuel temperature sensor, flow rate adjusting valve, purge valve, and the like may be connected to the control means so as to control the introduction of fuel into the purge tank, and various other modifications are possible within the scope of the present invention. Of course, it can be added.

It is a systematic diagram which shows the example of an embodiment which implements this invention. It is a systematic diagram which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel tank 2 Feed pump 3 Feed line 4 High pressure pump 5 Common rail 7 Injector 8 Combustion chamber 17 Feed line (line)
21 Purge tank
28 First purge line
31 Second purge line 34 Intake passage 35 Sub-injector

Claims (2)

In a fuel supply device for a liquefied gas engine, the fuel led from the fuel tank is boosted by a high-pressure pump and accumulated in a common rail, and the fuel is led from the common rail to an injector at the top of the cylinder and injected into the combustion chamber.
With a heat exchangeable purge tank line from the fuel tank to the high pressure pump,
A first purge line connected to the purge tank for returning hot fuel from the high pressure pump to the purge tank and extending from the common rail to return hot fuel from the common rail to the purge tank; A second purge line connected to the purge tank,
Wherein the purge tank, the fuel supply system of the liquefied gas engine, characterized by being configured so as to cool the fuel to the high pressure pump by the latent heat of evaporation of the heated fuel by air the heated fuel. 2. The fuel supply apparatus for a liquefied gas engine according to claim 1, wherein a sub-injector is provided in an intake passage that guides intake air to the cylinder, and fuel extracted from the purge tank is guided to the sub-injector .

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